Probably the most useful site for locating your Hardiness Zone is located here. Just enter your zip code and your Hardiness Zone will be shown.
The benefit of Hardiness Zones is that it provides a starting point for planning which plants can winter-over where you live. However, there are a few drawbacks to the Hardiness Zone Map. It does not consider day length (changes considerably the further from the equator you go), snow cover (moderates soil freezing and insulates roots), humidity, frost, or soil moisture. Probably the biggest drawback is that it does not consider how warm your summer will be. The classic example is comparing the Shetland Islands north of Scotland and southern Alabama. Both are listed as bewteen Hardiness Zone 8-9. However, the Shetland Islands are sub-artic and southern Alabama is sub-tropical. There are almost no plants that can grow in both places.
The variations in summer heat around the globe is what prompted the American Horticultural Society to create their Plant Heat Zone Map. The AHS Plant Heat Zones are listed from 1 through 12. The zones are based on the average number of days per year that the temperature will rise above 86 degrees F (30 C) as this is the temperature above which plants start to show heat stress. This is a great tool to augment the Hardiness Zones in your planning. You can dowload a PDF of the AHS Plant Heat Zones here. You can also search for your Heat Zone on this page by entering your zip code.
Here is a searchable map to find your Sunset Climate Zone, but I prefer going to the Sunset website and selecting the U.S. region here, as it provides a map as well as information on that growing region. Sunset also provides a pretty substantial searchable plant database for their Climate Zones on this page.
Combining Hardiness Zones, AHS Plant Heat Zones, and Sunset Zones, you will be able to more confidently chose plants that are well suited to your local conditions. These are great tools for planning your Permaculture System.
Here is a link to my article on Hardiness Zones for the World.
For my reference, I also want to add a Pacific Northwest Hardiness Zone Map as well. It is based on the 1990 data, but is still useful.